Heating structures for chromatographic columns



Dec. 6, 1966 T. c. DODD ETAL 3,290,482 HEATING STRUCTURES FOR CHROMATOGRAPHIC COLUMNS Filed Oct. 12, 1964 2 Sheets-Sheet 1 4 MANUAL CONTROL Ind/reef Direct ere E INVENTORS. TRAVIS C. 0000 JOHN B. R0550 BY CHARLES R. FERR/N %Z'Z&

ATTORNEY Dec. 6, 1966' 'r. c. DODD ETAL 3,290,432

HEATING swnucTurms FOR CHROMATOGRAPHIC COLUMNS Filed Oct. 12, 1964 2 Sheets-Sheet 2 INVENTORS'. TRAVIS C. 0000 JOHN B. R0550 M CHARLES R. FERR/N A TTORNE Y United States Patent 3,290,482 HEATING STRUCTURES FOR CHROMATO- GRAPHIC COLUMNS Travis C. Dodd, John B. Rosso, and Charles R. Ferrin, Tulsa, Okla., assignors to National Tank Company, Tulsa, Okla, a corporation of Nevada Filed Get. 12, 1964, Ser. No. 403,174 9 Claims. (Cl. 219-201) This invention relates to structures which bring chromatographic columns up to their operating temperatures evenly and quickly without overshooting the final temperature required. More specifically, the invention relates to structures providing a selection between a system including an oven for heating a column and a system in which the electrical resistance of the column is used to provide heat.

It is a basic decision between heating a chromatographic column by oven heat and heating by use of the electrical resistance of the column. Many factors determine this decision. It is desirable to be able to select between the systems. The prior art has failed to provide a convenient structure with which to switch from one such system of heating to the other.

Additionally, the prior art has failed to recognize the complete effect of temperature differences within an oven provided for a column on operation of the column. The prior art has failed to grasp the importance of maintaining a minimum cubic volume for the column and a corresponding minimum volume for the oven provided for the column. Further, the prior art has provided no system for regulation of heat from a heater positioned within the column coils to transfer heat uniformly and quickly to the surface of the coils.

The principal object of the invention is to alternately provide resistance heating and oven heating for a chr0- matographic column.

Another object is to provide a flow path for air over a heating element mounted within the reaches of a coil of a chromatographic column, and thereafter over the column, so as to uniformly heat the column as required to operate the column.

The invention contemplates a mounting for a chromatographic column which will accommodate a vacuum flask over the column to form the effective oven about the column. The heating element is mounted within the reaches of the coiled column itself. Bafiiing is then provided to direct air which is drawn over the heating element and the column in a pattern which will raise the temperature of the column uniformly and quickly to that level desired for operation.

Additionally, a circuit is provided to supply electrical energy to a column so the electrical resistance of the column will convert the electrical energy into heat. The two heating systems are linked by a selector station by which either the resistance heating or the oven heating can be employed on the same column.

Other objects, advantages and features of the present invention will become readily apparent from the following detailed description of the invention with a specific reference to the accompanying drawings, wherein;

FIG. 1 is an isometric representation of a partially sectioned structure of the top of a chromatograph cabinet with a column which can be either resistance heated or oven heated with structure in which the present invention is embodied; and

FIG. 2 is a sectioned isometric representation of an oven-heated column in which details of the baffies directing air over the column are shown.

Direct or resistance heating Referring to FIG. 1, there is shown the outline of a cabinet 1 within which is mounted the components required to operate a chromatographic column. Within a hole formed in the top of cabinet 1 there is mounted a platform 2 for the support of a chromatographic column.

Details of the mounting for platform 2 are not shown. For present purposes, it is deemed necessary only to indicate that column 4 is mounted to a conduit system through fittings 5 and 6 in platform 2. With this conduit system, samples are supplied column 4 and separated components are removed for detection by the units mounted within cabinet 1.

Column 4 is made of metallic tubing which offers suflicient electrical resistance to convert electrical energy into heat. The electrical energy is supplied through a transformer 7 connected across a line supply with an output connected to terminals 8 and 9 attached to the conduit system of column 4. The temperature to which column 4 is heated may be detected by a thermocouple 10 and read on a conventional meter 11.

It is possible to place meter 11 in control of the electrical energy supplied to heat column 4. To illustrate this automatic control, instrument 11 is shown as connectable to a control station 12 which is in series with transformer 7 and terminals 8 and 9. Alternatively the regulation of the power passed through control station 12 to column 4 can be set by manual control 13. Switch 14 can be positioned to connect control station 12 to the manual control 13 or the output of instrument 11. In either event, electrical power is supplied to column 4 and its temperature read from instrument 11. Therefore, the control over the power may be manual or automatic in accordance with the setting of switch 14.

General comments on the resistance heating operation When using resistance heating of column 4 the vacuum flask 20 is removed and the heated column simply comes into thermal equilibrium with the surrounding air. Generally, it is more economical to observe the temperature of the column by the reading on instrument 11 and adjust the manual control 13 as required to maintain, or change, the temperature. However, it is certainly possible to use a controller which will respond to the thermocouple 10 and maintain a predetermined temperature, or program of temperatures.

The real difficulty is with measuring the heat of the column directly. No way has yet been found to attach a thermocouple to a thin-walled chromatographic column without reducing the temperature measured some unknown amount. The accuracy of this detection of temperature is yet to be improved for satisfactory control in this analysis.

Oven structure Column 4 can also be heated by oven heat. A very simple, yet effective, oven is provided by vacuum flask 20 which is sized to fit snugly over the column 4 and platform 2. This vacuum flask 20 is basically cylindrical in form, its open end fitting to the platform 2 and having a volume only large enough to closely fit about the structure mounted on the upper side of platform 2. With the 3. column 4 coiled and spirally upward, the combination of both the column and oven-flask have a practical minimum volume.

When it is desired to cool the oven-heated column quickly, the flask 20 can be simply lifted from about the column. If rapid cooling is desired ambient air can be blown over the column. If temperatures lower than ambient are desired the flask 20 can be filled with cooled liquid and the column bent into the liquid.

Control of oven heating Heat for the oven is developed by a resistance heater not shown in FIG. 1. However, FIG. 1 does disclose controls for energy to this heating element.

Electrical lead 21 is the hot side of a power line to the heating element. This line goes to trigger board 22 which is, effectively, a switch with which the hot side of transformer 7 is connected to terminal 9 for resistance heating or the oven heating element within the reaches of column 4. The control of the power from transformer 7 is also through control station 12 for this resistance heating.

The temperature of the oven is sensed by bulb 23, mounted on platform 2. The signal from this sensing element is then taken to unit 24 and applied to the control of the power from transformer 7 when switch 14- connects unit 24 to control station 12. When unit 24 is in control of the oven heating, the switch of trigger board 22 will have to connect the power of transformer 7 to lead 21 through control station 12.

FIG. 2 shows the column 4 with the resistance heater mounted within the reaches of the coil and baflie structure directing heated air over the surface of the column. The assumption is that column 4 is to be heated within its oven. The electrical system supplying power to the resistance element within the oven is not shown. FIG. 2 is designed to teach how air is heated by the resistance element and guided into heat exchange with column 4. The supply of sample to column 4, the detection of the elements separated by the column, the electrical supply system for the heater, the detection of temperature for control of the supply system, these are important, of course, but not a part of the concept disclosed by FIG. 2.

It has been previously pointed out how column 4 is mounted on platform 2 through tube couplings. The reaches of the column spiral vertically upward within the volume of inverted vacuum flask 20. Perforated, cylindrical shield 27 is then extended up and closed at its upper end with perforated cap 28. This much was describable from FIG. 1.

Main stream of circulation Now, with the sections of FIG. 2, a vertical cylinder 40 can be seen as arranged concentrically within shield 27. This cylinder 40 is mounted over a hole 41 in subplatform 42. Rotor 26 is mounted below hole 41 so as to draw air downward from the top of cylinder 40 and discharge it from beneath the sub-platform 42 to the lower part of the oven.

Note that imperforate cylinder 40 is short of the lower face of cap 28. Thus a passage 43 is formed through which air between cylinder 40 and cylinder 27 is drawn to pass downwardly through hole 41. Also, the air passing down through the holes of cap 28 join the air through passage 43 and both portions pass down the inside of cylinder 40 and over resistance heating element 44 before passing through hole 41.

The complete, over-all path of circulation is now clearly established as down the inside of cylinder 40, up and around the outside the reaches of the coil of column 4, through the perforations of cylinder 27 and cap 28 and down the inside of cylinder 40 again. This is the overall plan of circulation of heated air within the oven of flask 20. This circulation will be compared with the 'well-known direction of distributed air from a plenum chamber over a column. However, it is now apparent that the circulation provided by this invention is far more complex. Also the results are far advanced over those possible with the prior art arrangements.

Closer analysis of the circulation system provided by the structure disclosed shows that the main circulation stream of heated air is traced from the discharge of rotor 26 up the outside of the reaches of column 4 and down through holes 45 in cap 28. From this main stream of heated air are drawn off the branches of heated air which complete the convection heating of the column.

Pressure and temperature gradient Obviously there is a pressure and temperature gradient in the air stream from the discharge of rotor 26. The pressure is greater at the rotor discharge than at the cap holes 45. Also there is a temperature gradient along this air stream path. The temperature at the rotor is greater than at the cap, The amount of air drawn off this main stream, and into the intermediate branches, for convection heating of the column, must be proportioned to heat the column evenly and efficiently.

Branch circulation streams There are two general ways to control the heated air drawn from the main stream and over the reaches of the column 4. The size of the holes in shield 27 can be varied or the number of holes per square unit of shield surface can be adjusted to give the desired results. Further, the position of the holes can be arranged to force the heated air drawn from the main stream to sweep over the surface so as to impart heat to the coil reaches uniformly and efiiciently.

In the actual reduction to practice, the holes 46 were increased in size they were formed in cylinder 27 in the vertical direction. Further, the holes were placed behind the reaches of the column 4 to draw the heated air around the cylindrical surface of the column. The result was a heat exchange between the heated air drawn from the main stream and the column which raised the temperature of the column as rapidly as; possible, and with uniformity. I

The branch streams of air from holes 46 in cylinder 27 are collected in the annulus between concentric cylinder 27 and imperforate cylinder 40. Only one exit is provided from this annulus and the air of the branch streams travels through this passage 43 to join the remaining air of the main stream as it-is drawn through holes 45 and down the bore of cylinder 40.

Heating by resistance 44 Heating element 44 has already been referred to. It is mounted within cylinder 40 and electrically connected to transformer 7 through hot line 21. More specifically, switch 47 on trigger board 22 can be positioned to connect hot line 21 to control station 12. The power from transformer 7 is then controlled into element 44 through stat-ion 12.

Actually, the element 44 itself is readily formed of a tube, or conduit, similar to the casing of column 4. This tube heats as readily as a solid wire and provides a relatively large surf-ace for exposure to the downcoming air within cylinder 40. Heat is thereby transmitted quickly to the air of the main stream.

To control the heat discharged by the element 44, shielding is provided by cylinder 40. This shield is effective to prevent radiant heat from element 44 teaching the column directly. Also, the fact that the branch air flows upward in the annulus between the shields 40 and 27 gives further positive insulation against heat from element. Therefore, the heat transmitted to the column 4 by conduction is controlled by the bafiiing to eflieiently and uniformly raise the temperature of the column to the working temperature required.

The over-all combination of structure produces the new result of the invention. The basic circulation of air over the heat source is controlled by the size of the holes in the cap 28 and the capacity of the blower 26. The heat input to this main stream of air is from the resistance heater 44. The temperature of the air is measured by bulb 23, placed in control of the electrical energy input to element 44. The branch streams of air are drawn from the main stream through the holes 46; in so traveling, they are brought into contact with the reaches of column 4 to raise the temperature of the column uniformly and quickly to its Working temperature.

Conclusion Little more is needed to a complete understanding of the invent-ion. FIG. 1 shows the column heated directly by the use of the column wall itself as a resistance element. The flask 20 is ordinarily removed and the temperature of the column sensed by a thermocouple. Trigger board 22 has switch 47 positioned as shown to place the column wall in circuit with transformer 7.

The alternate mode of heating is by placing the flask 20 over the column and connecting resistance element 44 in series with transformer 7. Switch 47 is then shifted to its alternate position on trigger board 22 .to give the required connection. The temperature of such oven is then measured by bulb 23.

Either temperature sensing element can be placed in automatic control of the heating with the proper position of switch 14. Also manual control can be exerted over either heating system by proper positioning of switch 14.

When the column is heated by a resistance element, the bathing provided insures the efficient, precise and uniform heating of the column. The column goes up smoothly and quickly in temperature and the highest value selected is not overshot; all because of the control the invention exerts over the convection heating.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the method and apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The present invention having been described, what is claimed is:

1. A system for heating a metallic chromatographic column, including,

a source of electrical power,

a metallic chromatographic column arranged in the form of a coil,

an electrical resistance mounted within the reaches of the coiled column,

a metallic chromatographic column arranged in the form of a coil,

a means with which to selectively connect the source to the resistance, within the reaches of the coiled column and to the column as a resistance,

and means for detecting the temperature of the column and automatically and continuously controlling the source to bring the column to .a predetermined temperature and maintaining the column at the predetermined temperature.

2. The system of claim 1 including,

a rotor for circulating air over the resistance and the column,

and baflling arranged between the resistance and column to direct the heated air over the reaches of the column coil so as to shield the column from radiant heat from the resistance while the temperature of the column is 6. rapidly and efliciently raised to its working temperature by the air flowing over it.

3. The system of claim 1 including,

means for manually controlling the source,

and means for selecting control of the source between the manual control means and the means for automatically and continuously controlling the source.

4. The system of claim 3 in which,

the means for automatically and continuously controlling the source includes a system utilizing a thermocouple directly sensing the column temperature and a system utilizing a temperature responsive element sensing air circulated between the electrical resistance and the column.

5. A system for heating a metallic chromatographic column, including,

a source of electrical power,

a metallic chromatographic column arranged in the form of a coil,

an electrical resistance mounted within the reaches of the coiled column,

a metallic chromatographic column arranged in the form of a coil,

a means with which to selectively connect the source to the resistance, within the reaches of the coiled column and to the column as a resistance,

means for detecting the temperature of the column and automatically and continuously controlling the source to bring the column to a predetermined temperature and maintaining the column at the predetermined temperature,

and a removable vacuum flask sized to fit rclosely about the coiled column to function as an oven when the source is selectively connected to the resistance to bring the column up to the predetermined temperature.

6. A system for heating a chromatographic column,

including,

a platform on which a chromatographic column is mounted in the form of a vertically extended coil,

a source of electrical power,

an electrical resistance adapted to be connected to the source of power for heating the resistance when the resistance is mounted within the reaches of the column coils,

an imperforate baflle formed generally as an openended vertical cylinder mounted between the resistance and the column coils to shield the column from radiant heat of the resistance and direct air flow over the resistance element,

a rotor mounted at the lower open end of the imperforate baflle cylinder to draw air down and over the resistance,

a perforated baflle cylinder mounted between the imperforate baffle and the reaches of the column coils to direct heated air from the rotor over the reaches of the column coil and into the annulus between the imperforate and perforated baflle cylinders and direct the heated air so collected to the top of the resistance to be recirculated over the resistance by the rotor,

and a perforated closure for the upper end of the perforated bafl'le cylinder to receive heated air not drawn over the column and through the perforations of the perforated baffle and direct such heated air into combining with the heated air from the annulus that both portions of the air might be recirculated together over the resistance.

7. The system of claim 6 in which,

the perforations of the bafl'le are arranged to direct air over the column so the column will be heated uniformly and efiiciently to its working temperature.

8. The system of claim 7 in which,

the perforations are sized and arranged to flow more of the heated air over upper reaches of the column coil than over lower reaches.

7 9. The system of claim 6 in which, the resistance is in the form of a coiled tube.

References Cited by the Examiner UNITED STATES PATENTS 8 OTHER REFERENCES Ashbury et al.: Versatile Gas Liquid Partition Chromatograph Apparatus, Analytical Chemistry, vol. 29, N0.

RICHARD M. WOOD, Primary Examiner.

ANTHONY A. BARTIS, C. L. ALBRITTON,

Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 290, 482 December 6, 1966 Travis C. Dodd et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, lines 59 and 60, and column 6, lines 22 and 23, strike out "a metallic chromatographic column arranged in the form of a coil,", each occurrence.

Signed and sealed this 2nd day of January 1968.

(SEAL) Attest:

Edward M. Fletcher, Jr.

EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A SYSTEM FOR HEATING A METALLIC CHROMATOGRAPHIC COLUMN, INCLUDING, A SOURCE OF ELECTRICAL POWER, A METALLIC CHROMATOGRAPHIC COLUMN ARRANGED IN THE FORM OF A COIL, AN ELECTRICAL RESISTANCE MOUNTED WITHIN THE REACHES OF THE COILED COLUMN, A METALLIC CHROMATOGRAPHIC COLUMN ARRANGED IN THE FORM OF A COIL, 